text:
RATO used to get civilian aircraft out of airports with inadequate runway length?
There are plenty of stories of large aircraft accidentally, or emergently, landing at airports that don't meet the plane's runway length requirements.  The only solution to getting them out that I've read is stripping them to the point that some authority deems them light enough for takeoff on the short runway.
What I haven't read of are the use of any measures to increase the thrust available for the takeoff run.  The first idea that came to mind was the use of RATO.  Is this possible with civilian aircraft?  Is it done?  If not, why not?
(My second thought was to temporarily install water injection.  But then I figured that by the time a system like that could be tested and approved the plane could have been disassembled for overland shipping.)

You'd be surprised how short of a runway you would need for a large airliner if it is unloaded and has minimum fuel. Usually if it can land there without damage, it can take-off again too.

When I was a teen, a 727 with an emergency of some sort landed at Moscow-Pullman airport -- a strip normally serving GA and 12-18 passenger turboprop regionals, nothing larger.  They had to bring in another pilot with short-field experience, but they got it out with enough fuel to get to Lewiston, ID or Spokane, WA, don't recall which...

The first thing that comes to my mind is crashing airframes left and right while failing to rescue hostages in the late 80s.

This video shows an empty 737 taking-off in just 2300ft. As Ron Beyer said, "Usually if it can land there without damage, it can take-off again too."

The DH Comet was equipped with RATO.
The Fairchild SA226 had a RATO bottle in the tail to improve single engine performance.  As I recall, removing the spades on the main landing gear eliminated enough drag to render the RATO unnecessary.
Boeing built twelve "727-200/JATO" variants for use by Mexicana Airlines.

The rocket installation was intended for emergency use only when
  flying out of a hot and high airport at maximum gross weight. Without
  the JATO, the aircraft would have to be payload restricted to account
  for the need to reach a safe altitude in the event of an engine loss
  after committing to takeoff. By having the JATO provision, Mexicana
  could operate its 727-200s at full payload. In the event of a loss of
  engine at past V1, the JATO unit would fire and allow the
  heavily-laden jet to reach a safe altitude and get aerodynamically
  cleaned up.

This old video shows a demonstration of that scenario with one of those special 727-200s:

The JATO provision was eventually made obsolete by later developments
  in the JT8D engine that featured "APR" automatic power reserve. It
  sensed a power decrease from one of the engines failing on takeoff and
  automatically boosted the power to the remaining two engines by a
  significant margin.

Some DC-9s also had RATO capability.

a) Hand-held camera shot of old VHS recording FTW! B) What are the "spades" on the MLG?

Just found more info on the 727-200/JATO.  And here's the best photo I've found of the system in action.

@FreeMan the spades were sheet metal plates affixed to the main landing gear legs.  When the retracted, the spades covered a hole on the underside of the nacelle.

Did those 727s ever have to use the RATO system in revenue service?

The same reason you give for water injection would apply to RATO.  The airframes are not structurally reinforced, nor are there any mounting points or wiring and switches needed for igniting them.  It would be a major endeavor to test and certify such a system for the rare occasions when someone might want to have that option.

Would not water injection bring engine to power output same as it is during low temperature (high altitude) operation?

I don't know very much about water injection.  I answered in the context of the major modification and certification required.  You seemed to discount water injection for that reason, and I just wanted to point out that installing RATO on an airframe not designed for this capability would require as much or more engineering effort.

The difficulty of engineering a RATO is only half the reason, the rest is that reducing weight is really effective.
Typically the empty weight of an airliner is about half the max take off weight. That means that it can accelerate twice as fast, only requiring half the distance to reach the same speed. Also, a lighter plane can take off at lower speeds (although not half, as lift depends on speed squared). Put the two together, and wait for the coldest part of the day when the air is densest and it could manage with about a third of the normal runway.

@llama Would you and the three people that upvoted your comment please get out a pencil and piece of paper and do the math. V=a * t. If V is constant and a is doubled, t is halved. x = 1/2 a t^2. Therefor new x = 2 * 1/4 old x. That's half the distance to get to the same speed. At the same distance and a doubled, t is .71 old t. v= 2 * .71 = 1.42. That part was correct.

Lift depends on speed squared, so at half the weight the aircraft needs 1/√2 the speed, but it can accelerate to 1/√2 in ½ the distance. So you have quarter the distance before even waiting for favourable weather.

RATO capability must be designed into the airframe to a certain extent, you need either built-in structural reinforcement and thermal protection or the ability to retro-fit it later. Built-in capability adds weight that airplanes would be lugging around, retro-fit capability costs money to design in, test, certify, maintain and train pilots to use it.  All this would add up to significant extra costs for what is best described as a very infrequent edge case. It's cheaper to very occasionally break up an airframe.


text:
How does maneuver g-load affect drag?
High-performance jets can use high-g turns to scrub airspeed and energy (e.g., in run-and-break landing patterns).
What is the relationship between the aggressiveness of a turn and the rate of decrease in airspeed?
For example, does the rate of decrease of airspeed in a turn depend only on the g-load, or is it also a function of the no-load airspeed/drag of the aircraft?  Is there some aircraft characteristic (e.g., something like "form factor") that describes the relationship?  Or is this a unique characteristic of each aircraft type?

The decrease in Airspeed is a result from lower Thrust than Drag (T<D).
It is convenient to use the Specific Excess Power (SEP) in this case.
\begin{equation}
SEP = \frac{dh}{dt} +\frac{V}{g} \frac{dV}{dt} = \frac{(T - D)V}{mg}
\end{equation}
Solving for the decreasing speed:
\begin{equation}
\frac{dV}{dt} = \frac{T - D}{m} - \frac{g}{V}\frac{dh}{dt}
\end{equation}
Now we can see the possibilities to reduce the aircrafts Speed (making dV/dt negative).

Lowering the Thrust (turning off the engines / using reverse thrust)
Increasing Drag
Climbing
Number 3 is not interesting in this case, since we want to land the aircraft. Therefore Number 1 and 2 are the most practical Solutions.
The Drag can be split up into the Zero Lift Drag D_0 ("no load") and your Induced Drag D_i ("load")
\begin{equation}
D = D_0 + D_i
\end{equation}
The Zero Lift Drag for a specific Configuration usually depends only your Flight Speed V_TAS and the density rho, which depends on your altitude.
(Note: Speedbrakes, Opening up Weapon bays etc. are increasing C_D0). (I would say C_D0 is one of the important "form factors" but has only a small effect on subsonic flight compared to the following form factor)
\begin{equation}
D_0 = 0.5 \cdot rho \cdot C_{D0} \cdot V_{TAS}^2 \cdot S_{ref}
\end{equation}
On the other hand, the induced drag is dependent on the current load factor n_z.
\begin{equation}
D_i = 0.5 \cdot rho \cdot C_{Di}(n_z) \cdot V_{TAS}^2 \cdot S_{ref}
\end{equation}
So the needed Lift L can be calculated with the load factor by multplicating the loadfactor with the mass of the aircraft and the gravitational constant
\begin{equation}
L = 0.5 \cdot rho \cdot C_L \cdot V_{TAS}^2 \cdot S_{ref} = n_z \cdot m \cdot g
\end{equation}
We can solve for the lift coefficient:
\begin{equation}
C_L =  \frac{2 \cdot n_z\cdot m \cdot g}{rho \cdot V_{TAS}^2 \cdot S_{ref}}
\end{equation}
(Side Note: So, to achieve higher load factors we need higher C_L -> unstable Configurations)
One important thing to see here is, that C_L ~ n_z. This Lift Coefficient is needed for modelling your Drag. I am assuming we have a quadratic Dragpolar (not correct, but good enough for explanations). For this case:
\begin{equation}
C_{Di} = k \cdot C_L^2
\end{equation}
Since C_L ~ n_z -> C_Di ~ n_z^2. So by increasing the load factor from 1 to 6 will increase our induced Drag by 35 times! (Therefore high g maneuvers are used)
But getting this factor k (I would call this the main "form factor") right is quiet difficult, so I am going to mention only some dependencies on it (More about the influences on the induced Drag can be read in Raymers or Roskams books). This factor highly depends on the form of your leading edge. For Round airfoils you can get a net suction force (=Thrust) on the Leading Edge (Commercial). This suction force can not be created that effectivly on Fighter Aircraft, since they usually have quiet sharp leading edges.
This factor can also be influenced by:
Higher Aspect Ratio -> smaller induced Drag
Taper
Flaps
Airfoil
Lift slope

Some other ideas to increase the Drag:

Moving the Center of gravity so aircraft gets too stable and therefore a lot of trim drag will be created
Post stall maneuvers

But the easiest and most effective way is just to fly high g's.

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text:
Why couldn't the co-pilot reach the rudder on Alaska Airlines 261?
Alaska Airlines flight 261 was an MD-80 that suffered a catastrophic horizontal stabilizer failure.  The CVR recorded the pilots some minutes after they first declared an emergency:

Completely inverted and still diving at a -9 degree pitch, the crew struggled to roll the plane, with the captain calling to "push push push...push the blue side up," "ok now lets kick rudder...left rudder left rudder", to which the copilot responded, "I can't reach it". The captain then replied "ok right rudder...right rudder," followed 18 seconds later by "gotta get it over again...at least upside down we're flying."

Granted that by then they were hanging upside down, but aren't the pilots strapped in with four-point harnesses?  I'm wondering:

What might have prevented the copilot from reaching the left rudder (but possibly still able to reach the right rudder)?
Why would the captain ask the copilot to push the rudders instead of just doing it himself?

The MD-80 uses a mechanical linked flight control system according to this article. This means, that aerodynamic forces of the control surfaces are transmitted directly to the control column. This can lead to very high flight control forces acting on the flight controls. From your wikipedia article:

only by pulling with 130 to 140 lb (580 to 620 N) on the controls did the flight crew stop the 6,000 ft/min (1,800 m/min) descent of the aircraft

Concerning your 2. question: Given this, it is obvious that the captain did not ask the co-pilot to push the Rudder for him, but with him. He coordinated their efforts in flying the airplane by quite literally joining forces as the control forces were too high for one man.
Concerning your 1. question: I do not know exactly, however I speculate that the co-pilot could not reach the rudder pedals because his seat was not properly adjusted (for example because he was not flying actively when the incident took place), and the rudder was pressed such that the left rudder pedal was farther away. This would also explain why the captain then stated to push on the right side, as he assumed that the co-pilot might reach that pedal as it was closer to him. But again that is speculation.

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text:
Why is a Cessna C560 circling Washington DC during the protests?
Right now according to FlightRadar24 there is a Cessna C560 circling Washington DC.

It took off from Manassas Regional Airport and has been circling ever since. No other identification is listed.
Is there any other way to find out what this plane is doing and why it would be flying now?

from a journalist: https://twitter.com/josephfcox/status/1267661141519433728
I don't think any strict confirmation can be found, but such flights have been performed on most major cities these days. these aircraft are usually equipped with stingrays/IMSI catcher and similar communication surveillance equipment.

FYI I opened a meta discussion about this question: https://aviation.meta.stackexchange.com/q/4105/1467 as much the subject interests me and I have followed it in my spare time, I question whether it can be considered on-topic here.

Such a perfect circle... is this some autopilot mode?

It's possible global.adsbexchange.com might show more info for such a flight.

Not sure why it isn't shown but the tail number is N557PG.

There are also Predator drones circling Minneapolis, although this one flew hexagonally, to be exact.

@JeffB: https://tar1090.adsbexchange.com/?icao=a71ab8

@Brad you must not have been drilled in two-minute turns.  :-)

According to the Washington Post, an unidentified C560 was also seen circling protests in Baltimore in 2015. The FBI stated the aircraft were theirs and "specifically used to assist in providing high-altitude observation of potential criminal activity to enable rapid response by police officers on the ground."
FlightAware shows the callsign of the flight over DC tonight as JENA120, consistent with the callsigns used by FBI flights during the Baltimore flights.

The FBI isn't going to admit "We use them in order to track everyone's phone in the city, and gather all of their calls, text messages, and network connections without a warrant".

Baltimore/DC is the test area for a Wide Area Surveillance system similar to the military's "Gorgon Stare" project.  The camera unit is built by a company called "Persistent Surveillance Systems".  It records everything on the ground around the aircraft at a very high resolution using multiple cameras.  Analysts can go back and zoom in on anything in the search area at a later date and track and follow individuals and their vehicles.

Bloomberg had an article about such a system on board a Cessna flying over Baltimore in 2016, by a company called Persistent Surveillance Systems.

@johndoe Don't think you'd need something as obvious as a plane circling overhead to do that.  They'd get the same info from the cell towers anyhow.  The plane is more likely there because they want visual info.

@Darrel: you missed the part in john's comment about "without a warrant". Law enforcement likes Stingray and similar devices because it allows them to bypass that pesky issue of having to convince cellular phone companies to hand over the info they want. Instead, they just pretend to be the cellular network and get the info directly. There is some debate as to whether a warrant is required when using a Stingray, but for now the feds say they don't need one, and only in a few states has any law been passed making the requirement of a warrant explicit.

@johndoe a jet flying at nearly 17,000 feet is not going to be doing any cell phone or text message tracking.

@johndoe they don't need a circling plane for that.

@johndoe An IMSI catcher is much more likely to be useful deployed near the surface than at 17,000 ft. And especially in Washington, D.C. of all places, it would be pretty trivial for the government to install as many of them as they want around the city out of view rather than flying them around on a jet.

I expect it provides communication surport to the people they have on the ground and tracks how many mobiles are in each area so the know where groups are forming.

@SnakeDoc can you please explain why that is the case, possibly in an answer?

@Bjonnfesk No, because it's not aviation related. Cell Towers are directional, designed to spread the signal outwards, not upwards. 17,000 feet is 3.2 miles into the air, well above any cell tower. Not only that, a Jet has to fly relatively quickly to not stall, which means the cell connections would have to swap towers constantly, which would not allow for a good "interception and tracking" environment. So, basically, it can't happen from a Jet.

@SnakeDoc You make good points. However, I must counter that there are devices like the Honeywell Forge Router (https://aerospace.honeywell.com/en/learn/products/satellite-communications/router) which connect to the 4G network, ostensibly "ideal for buisness jets" - is it conceivable that they could be able to monitor LTE traffic, if not GSM or GPRS? Perhaps in a manner not intended to monitor individual traffic, but rather the general trend, to establish the general mood of the protesters and attempt to predict where violence might occur? If so, cell phone tower swapping is not a problem.

@Bjonnfesk That particular device is for providing network connectivity within the airplane. The airplane must have a ground station (with tracking) or a satellite connection for this data, ie. it does not come from normal cell towers as the plane flies. Here's a decent partial explanation of why cell connections won't work in a jet flying at 17,000 feet and at couple hundred mph: https://www.cnn.com/2014/04/14/tech/mobile/phones-in-flight/index.html

@SnakeDoc Pardon, that was not quite the correct product. https://www.reuters.com/article/att-inflight/att-honeywell-to-launch-4g-in-flight-broadband-system-idUSWNBB047WB20140428 | Page 3, under "Wired Data", it claims to be GSM and LTE compatible, and have dual-sim capability. https://aerospace.honeywell.com/content/dam/aero/en-us/documents/learn/services/flight-services/brochures/C61-1832-000-000_GoDirect_Aircraft_Data_Gateway-bro.pdf
"Client antenna connects to Wi-Fi or cellular based on selection" (emphasis added)

@Bjonnfesk some "base stations" are cell towers with their directional antennas pointed towards the sky. A lot of domestic flights with in-flight entertainment use this option since it's a lot cheaper and faster vs. satellite. However, these aren't normal cell towers and cell phones can't connect to them directly. To snoop calls and data, you have to MiTM the cell tower and your device, so cell phones connect through your snooping device. You read the data, and forward to the actual cell tower and the user can't tell the difference. Not easy, and you'd have to be really close to the user.

@Bjonnfesk continued... Your phone looks for the closest, strongest cell tower signal that's compatible, and connects. StingRay and other similar devices pretend to be a cell tower, and via proximity appear to be the strongest, closest signal to your phone. Your phone connects, and then the StingRay operator can see all your data and listen to your calls while forwarding them to the actual tower. In the OP's case, this jet is 99% likely providing visual surveillance with cameras and the good old Mk.I Eye Ball. ;)

Eloquently said. I concede :P. Thank you for clarifying. It happens too often that people simply assert things without providing any reasoning behind their assertions; I'm glad to see that you have knowledge to back up your position.

That plane was N557PG, a Cessna Citation V which is, according to the FAA, registered to National Aircraft Leasing Corp. That company is probably a front company for the FBI. Here's the track that N557PG flew on June 2, 2020. Compare to the image in your question:

Here's a link to see that track yourself. Note that it is probably only good until July 2, 2020 (about 30 days after June 2): https://tar1090.adsbexchange.com/?icao=a71ab8&lat=38.785&lon=-77.308&zoom=10.2&showTrace=2020-06-02
All the commercial trackers, like Flightradar 24, will hide aircraft identification info if requested (and paid) to. ADS-B Exchange is probably the first place anyone should check if they want to know what's flying around, because it has good coverage (maybe not as good as the commercial trackers) and never censors any information. Use https://tar1090.adsbexchange.com/.
After the 2015 Baltimore protests over the suspicious death of Freddie Gray while in police custody, it was found that the FBI had been flying more than a hundred aircraft over U.S. cities as part of a secret aerial surveillance program, where those aircraft were registered to front companies to hide their relationship to the FBI ("FBI behind mysterious surveillance aircraft over US cities" by Associated Press). National Aircraft Leasing Corp. was one of those front companies. You can see from the FAA registration database that there are 7 other companies, all fronts, with aircraft registered to the same address:

We know the flights are at least collecting video (including thermal/IR) surveillance because the FBI released some of it:

 (FBI archive link: https://vault.fbi.gov/protests-in-baltimore-maryland-2015/unedited-versions-of-video-surveillance-footage/1D3001Part1). We know they have the equipment to do other sorts of surveillance too.


text:
How do I calculate aircraft range with these parameters?
The parameters are:
MTOW, MLW, MZFW, OEW, maximum fuel weight, fuel flow rate and true airspeed. Measured in lbs and kts. Not given drag so unsure how to apply Breguet equation. Trying to construct a payload range diagram!

If you combine the amount of kg fuel used per seconds with total fuel available you can calculate the total possible flying time. If you know how long you're flying at a certain velocity, you can calculate the distance traveled.

In addition of @ROIMaison remark, assuming you don't have the fuel flow rate, you cannot calculate the range without the L/D ratio. It would be like trying to find the range of a car without knowing the slope angle of the road.

If the fuel flow rate and the true airspeed are for the same polar point, the answer is easy. You cannot, however, determine if this is your maximum range because you do not know any other points of the polar.
Your fuel consumption is MTOW - MLW. The flow rate will give you the flight time when you divide the fuel by the flow rate. With the flight time you can calculate the range by multiplying it with the airspeed. Hint: Convert all data into metric first so you don't screw up the calculation.
The maximum range can be done the same way using MTOW - MZFW for the fuel mass. MZFW - OEW will tell you how much payload remains at this point. The only impossible part is the transfer range point - use the maximum range and assume that the aircraft will fly as far with a lower take-off mass as with MTOW.
The Breguet equation will not work in this case.

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text:
Can pilots use PAN PAN Medical, even if they were not on MedEvac mission?
If there is a medical emergency on board, on a passenger or crew member, will the crew be cleared to use PAN PAN/MAYDAY MEDICAL on their R/T?
Is there any DOC in which regulates these phraseology?

The UK CAA Radiotelephony Manual (CAP 413) has the following to say about it:

PAN PAN MEDICAL is not used in the UK but refers to a Geneva
  Convention term associated with medical transportation by parties
  involved in a conflict.
Use of this term is not appropriate in the UK.

Which seems to be a pretty definitive no. Personally, I'd not heard of the term but assuming the CAA's interpretation of the ICAO's definition (i.e., for use during war) then I can't imagine it ever being appropriate outside of that use.
That said, why would you need to? Using a normal MAYDAY or PAN call and describing the emergency as a medical one is perfectly acceptable and would be fully understood by all parties.

The last paragraph is the definitive answer.

No. The phrase 'PAN PAN Medical' is reserved exclusively for medical transports. From ICAO Annex 10 to the Convention on International Civil Aviation- Aeronautical Telecommunications Volume II:

For the purpose of announcing and identifying aircraft used for medical transports, a transmission of the radiotelephony urgency signal PAN PAN, preferably spoken three times, and each word of the group pronounced as the
French word “panne”, shall be followed by the radiotelephony signal for medical transports MAY-DEE-CAL, pronounced as in the French “médical”. The use of the signals described above indicates that the message which follows concerns a protected medical transport.

However, the pilot can use PAN-PAN followed by request for medical advise if the situation is urgent. According to FAA Air Traffic Organization Policy, Air Traffic Control, PAN-PAN is used in case of urgency.

A pilot who encounters a Distress condition should declare an emergency by beginning the initial communication with the word “Mayday,” preferably repeated three times. For an Urgency condition, the word “Pan-Pan” should be used in the same manner.
PAN-PAN- The international radio-telephony urgency signal. When repeated three times, indicates uncertainty or alert followed by the nature of the
urgency.

So, PAN-PAN followed by request for medical advise is ok.

It's worth stating that a pilot who is experiencing a medical problem should call a mayday whereas if it is a passenger having a medical problem it's a pan-pan.

@GdD, I believe a passenger with medical problem might warrant a mayday too if the problem is life-threatening, no? Of course the bar is much lower for pilot.

Mayday calls should be reserved for problems that impact the safety of the flight, and a passenger illness generally doesn't count. It's really moot, if you tell ATC you have a seriously ill passenger you will get priority.

I would agree with Jan Hudec here. Mayday is a distress call that should be used when the aircraft requires immediate assistance (CAO  Phraseology  Reference  Guide). If a passenger is in immediate life danger, I would most likely declare an emergency with a mayday call.

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text:
When receiving a TCAS RA, DESCEND DESCEND, and starting the descent, if a pilot received GPWS warning, TERRAIN, what would they do?
The TCAS warning says: " DESCEND, DESCEND" and immediately after the crew receives: "TERRAIN, TERRAIN", what would they do?

Best guess: they would panic

I would prefer to take on the other aircraft rather than the terrrain, but that's just me.

Flip around, then nose 'down', like proven in a recent movie

TCAS (II) does not give the descend RA below 1200 ft AGL while climbing or below 1000 ft AGL while descending.

Image from FAA Advisory Circular 20-151A Table 2
In case such an unlikely event happens (and is not an equipment malfunction), the best possible maneuver is to climb away from the incoming aircraft i.e. turn and climb to the side of the previous route.

EGPWS has a "look ahead" feature so can give a terrain warning even if you are not within 1200' AGL....

@Lnafziger, the table implies that it should switch to TA ("TRAFFIC, TRAFFIC") in that case.

I would pull up and once in a stable climbs I would turn in either direction in this situation. If I get a warning to descend it is to prevent a conflict with another aircraft, whereas a terrain warning is to prevent impact with the ground. The ground is much bigger than another airplane, so the lower risk is collision with an aircraft. In other words, if I descend I will certainly hit the ground, if I climb I may hit another aircraft, so climbing wins. Turning in either direction will hopefully decrease the collision risk.
It would suspect this is an unlikely situation, TCAS should not give an instruction which would put you into another conflict.

Wouldn't turning increase the probability of crashing with the ground and/or the aircraft?

If the aircraft is climbing then contact with the ground shouldn't be a concern if turning. If you fly straight ahead then you will potentially be putting the aircraft into conflict again, so while turning could potentially increase the possibility of collision it has a greater chance of decreasing it.

Makes sense. Also wouldn't it be better to instruct the aircraft above to ascend? what is the likelihood of this ever occurring?

This scenario is pretty unlikely as I don't think TCAS would say to descend if it was going to cause a terrain warning. As for communicating, that's actually a bad idea as it could cause confusion. See the Underlingen disaster as an example of that.

@GdD If the aircraft is climbing then contact with the ground shouldn't be a concern if turning. <-- Depends on the terrain. For example if you got a GPWS alert in a canyon because the floor is rising making a turn (even in a climb) could cause you to impact the canyon wall. I'd wager the climb and the chance of hitting another aircraft would still be preferable to a descent and the certainty of hitting terrain though: You've got a better chance with Big Sky than you do with Big Dirt.

If you are in a canyon and receive both GPWS and TCAS alerts, maybe panicking is your best option?


text:
Is there any reason on passenger airliners not to have a physical lock between throttles?
A physical lock so one throttle can control all of them. Sure there would be circumstance to disconnect it such as engine failure and possibly wind shear but there really too many instances of pilots and occasionally system failures causing one engine to not track other  engine(s) output and at very least cause a significantly increased workload and contribute  to severe accidents. So what isn't it physically interlocked?

Does there need to be a better reason than 'every single engine failure now becomes a twin engine failure because you have to take both throttles to zero'? This will indeed avoid problems associated with asymmetric thrust but replaces them with some other rather substantial ones.

And even more for something like the B-52, with eight engines, and (if I understand correctly) throttles that aren't physically coupled. One would think it is quite easy for the pilot to accidentally lose grip of the leftmost or rightmost throttle when trying to move them in synchrony.

Simply said - you don't need it, as on the normal throttles you can grip both with no problems. Second - you can use it to "walk the throttle" by adjusting only one while using the second as a reference/hold.

Most twin-engine prop aircraft run with the throttles slightly offset all the time to eliminate the "thrum" of props beating the wind every so slightly out of rhythm. There are many twin-engine props used today as "passenger airliners".

If I'm not mistaken, engine start is generally one at a time.

"there really too many instances of ..." can you back up this assertion (with statistics or concrete examples)? I believe such cases are extremely rare to the point of being practically nonexistent. Locks are a (bad) solution without a problem.

https://www.reuters.com/article/idUSN01319038 Sriwijaya Air 182, AF091. ..

If there is any safety case against something, there has to be a really good reason for adopting it. This seems to lack any good reasons, and to have potential to cause several different safety problems. That makes it a bad idea.

The problem with physical locks:
A locking device can fail "on" (same reason carbureted piston engines use primer systems instead of chokes) so you are stuck with both/all levers ganged together, which can be a problem in an engine fire situation. So it's out of the question for that reason alone.
The other one is, except with the latest FADEC engines, the throttle/thrust lever is a mechanical connection with rigging allowances, connected to a hydromechanical (with electronic trimming on newer engines) fuel control system. Much of the time the two levers are not perfectly matched when Torque or N1 or EPR values are matched (often it's just from having a low time engine on one side and a high time engine on the other side).
Another minor factor is when moving the levers in small increments, you "walk" them along which makes it much easier to make very fine adjustments, which you couldn't do if they are locked.
So overall, there are safety show stoppers, and the concept isn't really desirable operationally.

Why make fine adjustments?

To avoid crashing the airplane?

You are often tweaking the levers to make tiny changes. Say on an approach you are 6kt fast, you need to make a very small thrust reduction, then wait for the result.  That's how you avoid chasing the thrust/speed all over the place.  Walking them back makes that much easier. You're using one lever as an anchor to rotate your hand to make a tiny movement in the other, then vice versa.


text:
Are dual input situations for major aircraft quite unusual?
Why would the Captain and Co-pilot both need to control the plane at the same time in normal operations? The only time that I could think of one is manually flying and doing complex maneuvering and they want to switch because of the difficulty but sounds really risky with it being much better to stabilize and then switch.

what's "major aircraft"?

Are you considering fly-by-wire aircraft only, or only manual flight controls, or both? Are you considering inputs to the same control element or to different elements by the two pilots?

This should be rephrased so that it's not asking for an opinion-based answer. I think this could be salvaged if it was asking about the technical details of dual-input scenarios.

I don’t know if it is still done, but in my younger days, Huey (UH-1) pilots in low hovers on gusty days would often ask their copilots to be hands-on with them.

Define "quite unusual".

Usual- a rare cicumstance.

Where on earth did you get the idea that they would ever control the plane at the same time ?
Not only does it make no sense from a purely practical perspective, but also its basically a big fat no-no.
During training, you spend a lot of time on the psychology and practicalities of MCC (Multi-Crew Cooperation).  To cut a long-story short, you learn the PF/PNF (Pilot-Flying/Pilot-Not-Flying) system and that's the way you work for the rest of your career.
Designated PF does the flying. Designated PNF does everything else (radio, nav, computers). PNF will also call out items that need to be cross-checked (e.g. items that get displayed on both PF and PNF monitors).
PF and PNF roles switch throughout the flight depending on operational or human requirements.  The switch is very explicit with verbal confirmation of donation and acceptance of the role.

And when people don't respect the rule, this happens: "Robert responded to this by saying, "controls to the left", and took over control of the aircraft. He pushed his side-stick forward to lower the nose and recover from the stall; however, Bonin was still pulling his side-stick back. The inputs cancelled each other out and triggered an audible "dual input" warning"

I have seen instances protrayed in aircraft accident recreations where the control surface hydraulics have been compromised and both pilots were simultaneously trying to muscle the aircraft controls.

You mean the formerly flying pilot as he transitioning to the monitoring pilot  would suddenly let the controls go and expect the flying pilot to be in control with the rudder and control surfaces exactly in the right spot. The question is dual input not continuously be in dual control.

In abnormal situation, such rudder control problem,  pilots have had both push the rudder with all their might just to have some control- dozen of other scenarios where two pilots are giving flight inputs. I wouldn't want you in a plane- you'd let the plane crash,

The Me-321 prototype had only one pilot. After the first flights, this and all subsequent airplanes of the Me-321 and 323 production had two. This giant plane simply required too high control forces for a single pilot, and two were needed to fly the airplane properly.
Being a glider, the 321 had manual controls despite its 55 m wingspan. Besides the second pilot, electric flaps were added after the first flight as well.

Why would the Captain and Co-pilot both need to control the plane at the same time in normal operations?

Because the fully reversible controls require more strength than a single pilot can muster.

what makes a Me-321 a "major aircraft"?

@HiddenWindshield Do you have any proof for your claims? Did you speak to people who have flown the type (as I have done, admittedly decades ago)?

@PeterKämpf Apparently I misread. The electric servomotors were only used for the flaps, not any of the other controls.

@HiddenWindshield … as I said in my answer. Gliders normally do not use powered controls, even with 55 m wingspan. Adding a second pair of hands is both easier and adds less mass, after all.


text:
Can military radar detect all civilians aircraft at inflight altitudes regardless of transponder status?
Not the same as this one Can radars detect all planes, including military ones? because it implies civilian radar systems.
Simply military radar systems must be able to detect all civilians aircraft at normal inflight altitudes and any aircraft near secure areas even if they can't necessarily determine their status. Low level probably used for criminal purpose aircraft probably can't be easily detected. Can military radar systems really spot civilian aircraft at say 1000 plus?

Miltary radars surely what have higher quality primary radars than civilian radar and staffed by more experienced operators. ATC is mostly more used to secondary radar and all that aircraft management stuff.

Not interested in ATC primary radar capacity. Sure it will depend on the country/ military radar system currently in use but that is for answerers to choose the system employed.

@mins, country and source for the disappearance of civilian primary radars? To my knowledge FAA radar sites are (almost?) exclusively combination PSR/SSR models. Primary targets are required to be depicted on the scope at all times unless the controller's area of jurisdiction includes only Class A airspace.

@randomhead: See this answer. For France, the sites for civilian PSR and SSR are shown on this document. Civilian PSR are used mainly for busy TMA. This other document is in French, but page 48 you can see how are currently satisfied the needs for different traffic densities, most PSR are optional. PSR might be replaced by passive MSPSR in the future.

"staffed by more experienced operators" Everyone is a rookie when they start out, military, civilian, or otherwise.

Primary radars (PSR) used by military can detect civilian aircraft exactly the same way, and with the same limits, than they detect military aircraft.
The SSR transponder of civilian aircraft plays no role in this type of detection. Note military aircraft also use transponders.
For a primary radar an aircraft is a reflective target, the larger the better. So it's actually easier to detect large civilian aircraft than small military aircraft. One important criterion is the radar cross section (RCS) of the target, this is the target area required to produce the echo the radar senses. Depending on the geometry, the material, the wavelength used, etc, this area may be smaller than the actual target cross section area.
For reference an octahedral corner reflector 45x45 cm used on boats has a mean RCS of 3.5 m².

RCS for a S band monostatic antenna:
$$
\begin{array}{|r|l|}
\hline
RCS & Object \\
\hline
\text {100 m²} & \text {Ship} \\
\text {50-100 m²} & \text {Large body a/c} \\
\text {10-50 m²} & \text {Medium range a/c} \\
\text {2 - 10 m²} & \text {Large military a/c} \\
\text {1 - 2 m²} & \text {Small military a/c} \\
\text {1 m²} & \text {Human body} \\
\text {0.1 m²} & \text {Missile, stealth bomber} \\
\text {0.01 m²} & \text {Drone, stealth fighter} \\
\text {0.001 m²} & \text {Shell} \\
\hline
\end{array}
$$
Source for values
The table says a medium-sized commercial aircraft is more easily detected, by 10 times, than a small military aircraft.
Some countries share the radar antennas between civilian and military, for example, Switzerland, a small and mountainous country, just uses all radars for all purposes, in a whole system named Florako (also on Wikipedia).
The major advantage of using a primary radar is its ability to detect targets without their cooperation (transponder answering the interrogator). The cons are its cost, the power required and:

A limit in distinguishing aircraft in crowded airspace. A secondary radar using individual airborne transponders is more powerful.

A potentially lower azimuth accuracy than SSR (secondary radar).

The inability to determine a precise altitude, though some short range PSR are specially made for this.

The difficulty to detect very close targets. It uses a single frequency for transmission and reception, therefore a close target echo may reach the antenna while the radar is still transmitting, and be ignored. This problem doesn't occur with SSR where the ground station and the airborne transponder transmit on two separate frequencies.

The difficulty to detect very remote targets, due to field intensity attenuation with the square of the distance. A SSR transponder generates a separate stronger signal for the return trip. However some primary radars offset this attenuation using huge transmission powers. After solving the problems created by the larger power they have a larger range than SSR, which don't need extreme ranges and use smaller power levels.

Both PSR and SSR are limited by the radio horizon, e.g. for a station at a height of 100 m, the radio horizon is about 47 km. This distance can be reduced by natural obstacles, like hills, and built obstacles like wind turbines. Aircraft can use this protection to fly "below the radar". To prevent this radar stations must be sited at the top of hills and peaks and secondary (mobile) stations sweep valley areas. A station at a heigh of 2,000 m has its radio horizon at about 210 km (calculator, add 1/3 for wave refraction in troposphere).

Some military primary radars use the lowest frequency bands for trans-horizon detection of missiles. They are de facto able to detect larger RCS targets, including any aircraft, but with a low azimuth precision.

New radar types, said multi-static (MSPSR) are able to detect echo from targets illuminated by sources other than their own antennas. This increases the detection ability, including for stealth aircraft. Other sources include cellular phone stations and TV broadcast towers, but also distant radars. MSPSR can be passive, not emitting any signal, but still be more effective than monostatic active stations.

Mind that technically a secondary radar is not a radar at all but an RDF system with benefits (in that it can analyse the signal it tracks, not just detect it).

@jwenting: I agree it would have been more clear to use radar only for natural echo methods, but SSR is still a method for detection and ranging by radio. Most people in my country use radar to talk about lidar speed measurement for cars, and "GPS" to talk about any localization system, including Galileo (!) or cellular networks.

I know, just wanted to clarify the difference between the technologies for people not familiar with them.


text:
Do services still apply foam carpet on belly landings?
From decades I have been reading that, fire services would spray foam on the runway, in order to avoid fire, on a belly landing. Is this procedure still being used? If not, what would be the safest procedure?

Recent gear-up landing (that was known in advance so emergency services could prepare) was LOT B763 at Warsaw on Nov 1st 2011. However I can't quickly find definite statement whether they foamed the runway in advance or not in the report (I believe they did not).

I have heard (probably here, but have no supporting documentation) that they no longer foam the runway so they don't use it all up on the runway and have none left for a fire that may break out on impact. There's a certain amount of logic to that (don't waste the foam if there isn't going to be a fire), but quite a bit of fallacy in it, too (they're really not going to plan that poorly, are they?).

Firefighting services still apply foam path, atleast outside US, though the practice is no longer encouraged.
FAA, in its 2002 CertAlert 02-04 actively discourages it:

The FAA does not recommend the foaming of runways for emergency landings and warns against the practice with any foam other than “Protein” foam....  It is recommended that ARFF personnel decline to foam a runway when requested by a pilot because they do not have the specialized equipment and protein foam

FAA lists a number of reasons for this decision (It had actually recommended foam paths for emergency landings in 1966, before withdrawing it in 1987), including,

Time may not be always available for foaming
The use of foam in foam path should not affect the subsequent firefighting abilities.
Foaming the runway should not affect the movement and safety of other aircraft.

ICAO too, does not recommend for foaming the runway in its Airport Services Manual, stating,

15.1.2 The effectiveness of runway foaming is not fully substantiated by the real evidence of operational incident studies.

ICAO also considers the various reasons for foaming the runway and analyses them:

a) Reduction in aircraft damage. ... The data available from a study of emergency landings made with, and without, the application of foam show
  that no significant reduction is achieved in the risk of fire or in the extent of damage by the foaming of runways.
Reduction in deceleration forces. ... It is to be noted that from what is
  known to date, the braking action of an aircraft on a foamed runway will only be slightly worse than that on a wet runway, assuming non-freezing weather.
Reduction in friction spark hazard. ... tests have shown that aluminium alloy metals produce no friction sparks capable of igniting aircraft fuel vapours ... on either dry or foam-covered concrete or asphalt runway surfaces. ... Titanium friction sparks, capable of igniting aircraft fuel vapours, could not be effectively suppressed by runway foaming in any of the scale research tests ...
Reduction in fuel spill fire hazard. From all that is known of the fire suppression qualities of foam and the scale research tests, it is clear that a foamed runway would have no appreciable effect on the fire hazard of fuel vapours in the atmosphere over the foam.

ICAO also points out that the primary firefighting vehicles should not be used for foam laying operations; Also, the time taken for the operations and replenishment is a concern.
It is to be noted that, though the practice is no longer recommended, fire services are not barred from using it if the pilot asks for it and facilities are available.
In a related note, US armed forces seem to use it.

Another reason they might add after Asiana 214 is that survivors may be hidden in the foam and be run over by emergency vehicles

no significant reduction is achieved in the risk of fire or in the extent of damage. This is the key point.  The Royal Air Force used to use Manston in southern England for landing "gear up" on a foam carpet but stopped when they found it made no difference to the outcomes.


text:
What does "alpha floor" mean?
I was talking to a pilot, and he said that the alpha floor had been activated, and I did not have time to ask him to explain this. So, can you clarify my doubt, please?

Related: Just wondering how you can get an Airbus into Alpha Floor?

Who do you work for? This is a concerning question.

Alpha floor is a thrust function which provides TOGA thrust regardless of thrust lever position in Airbus. From Airbus Technical Digest FAST 20:

Alpha Floor is a low speed protection (in normal law) which is purely an
  autothrust mode. When activated, it provides TOGA thrust. As the aircraft
  decelerates into the alpha protection range, the Alpha Floor is activated,
  even if the autothrust is disengaged. Activation is roughly proportional to
  the rate of deceleration.
... at low speeds, if a rapid avoidance manoeuvre is required to avoid terrain, windshear or another aircraft, it is safe to rapidly pull the sidestick fully aft and/or bank and hold it there. The aircraft will pitch up
  to max Alpha, engage TOGA thrust and climb away.

Note that this protection is only available under normal law and is lost under alternate law.

However apparently A310 already had alpha-floor, though it did not yet have fly-by-wire nor normal law. Not sure whether A300 had it too, but it probably did; A310 is not that much different from A300.

@JanHudec Looks like A300 did have alpha floor.

How should the rapid avoidance manoeuvre look in an Aircraft without alpha floor?

@curious_cat The pilot will have to add power using the throttle lever, and use the stick to reach the desired attitude without stalling.

When the angle of attack limit is reached, a value which is dependent on the configuration and longitudinal wind gradient, the FMGC receives the order from the FAC. This order is only taken into account by the FMGC, if:

Landing gear shock absorbers are extended at takeoff
and up to 100 ft at landing

If these conditions are met, the A/THR is engaged, and the Alpha floor protection is activated. The A/THR is commanded max. consequently.
The only way to cancel alpha floor is by disengaging the A/THR function.


text:
Is white/brown-out effect hazardous during the landing roll out?
Landing on unpaved runways or runways covered by snow or dust causes a white/brown-out visibility restriction.
Does it disrupt the pilot's visibility during the roll out in a fixed-wing aircraft?

In my experience landing single engine tractor, high wing airplanes on very dry, dusty sand and clay surfaces, as well as snowy surfaces, no. I think the danger lies in visibility impairment to rotorcraft pilots, as well as FOD damage to airframes or powerplants.

Whiteout can be a significant hazard to aircraft using reverse thrust to slow.


text:
Is it possible to fly with throttles staggered?
Does the autothrottle realign the throttle lever positions? If the throttle is staggered, does it mean that there is an issue on the engines?

You can fly in extremis with an engine entirely disabled.

Yes it is possible - as mentioned in a comment, most multi-engine aircraft can (fairly) happily fly with one engine at idle or disabled entirely.
Some autopilots will use some asymmetric thrust for yaw trim, and others will use asymmetric throttle settings to compensate for the engines producing different amounts of thrust. Those sound similar, but aren't quite the same thing.
For example here's a description of that happening on the 777. Neither are ubiquitous and both depend on the aircraft.
http://www.flight.org/the-boeing-777-thrust-asymmetry-compensation-tac
Note that two engines can never be identical, there will always be some level of asymmetric thrust. Traditionally this was countered with rudder trim, but newer aircraft sometimes adjust the throttle instead, as per the above link

On 747-100/200 aircraft with no auto-throttles (or no auto-throttle usage if the particular airplane had that), the flight engineer typically set power using either EPR or fuel flow. I never saw the thrust levers line up exactly.


text:
Is there any cockpit procedure used to avoid shutting the good engine, instead of the bad one (on fire, for example)?
Reading some reports, about the failure of crew members to fully understand the fault on engines, rarely, but it happens, the crew can misjudge the engine on fire, shutting down the good one. On airlines where you fly, is there any standard procedure to avoid this event, I mean, shutting the good engine, instead of the bad one?

The question that Simon points to is itself marked as duplicate, however the answer given in it before it was so marked is the answer that I believe would be given here, so I agree with this duplicate marking.

@CGCampbell After reading your comment I've just nominated the linked question to be reopened. I don't see any reasonable way that a question about shutting down an engine can be a dupe of one about bank angles. It looks like over-generalizing to me. Others may disagree, of course :-)

I'm not sure about a standard procedure, but I was taught to say aloud "dead leg, dead engine", meaning that the leg you are not pushing with to maintain directional control is the one with the problem. Only works on twins of course, and only if they have lost power.

This video might be interesting: note that both pilots have to agree (affirm) before 1) thrust to idle, 2) engine master switch off and 3) engine fire switch on.

As a PPL, I was watching a CFII in a twin-sim when he was given an engine out situation.  He ended up shutting down the good one.  When we talked about his thinking later, one major factor was that in his mind, one engine was dead... and you don't bother giving control inputs to a dead engine. (kinda seems common-sense, right?)   So he ended up going through the shutdown sequence, but on the good engine.  Obviously, task saturation was another major factor.

Procedures exist
If you read about the Kegworth crash you will see that the pilot started to follow a procedure he has been trained on but was interrupted by an ATC call and failed to complete the procedure. The procedure involves checking the engine vibration meters and reviewing decisions.
So, yes, procedures exist.

Procedures vary
Procedures vary depending on exact aircraft model and on the airline operating the aircraft. Some airlines use more memory checklists than other airlines. So it isn't possible to list a specific procedure that is used by all pilots of multi-engined aircraft.
Identifying problems
Pilots don't start from the point "we need to shut down engine No 2" they start from some observable event like "smoke in the cockpit" (as in the example incident above)
There are instruments on the instrument panel that show engine temperatures, vibration and other parameters that should usually make it evident which engine is not performing normally.
Here's an example procedure - note that this isn't the one for the airline and plane model in the incident above but it is probably similar

Note the points

Eliminates No 2 engine as source ...
...
Eliminates No 1 engine as source ...

There are also the instruments which might be able to tell the pilot(s) if an engine is goofing up.

The main problem as I recall was that their systems knowledge was not up to date on the 734 and they had received no type training.  On 731, 732 and 733, cabin conditioning air was drawn from engine 2.  On the 734, it is drawn from engine 1.  They could smell smoke co-incident with the engine failure and the bad systems knowledge was a strong driver in their decision that engine 2 had failed.

@Simon: Yes, however the Q was "are there procedures" - so I decided the actual contributing factors in this incident were not especially relevant to my answer.

I still have a question: Suppose, engine number 1 fire (twin engined aircraft). For any reason (poor training or poor CRM), the crew shut the engine number 2 down. TO AVOID THIS, is there any procedure (standand one) to be followed, to avoid this to happen?

@user12207: See update

The point is to be sure that the affected engine is shut down. Boeing has inserted a recommendation for that in their Flight Crew Training Manual (FCTM), mentioning explicitly:

Mistakes were done in the past.
Don't hurry in the engine shutdown.
PF must coordinate with the PM in the procedure.

The procedure also includes to retard thrust on the affected engine slowly. It gives time to feel something unexpected, like the aircraft loosing power on both engines (for a twin).
You can find such recommendation in the Boeing 737 NG FCTM and the 777 FCTM, like this one, page 308 (this is logical page 8-8 in both manuals).
Recommended technique for in-flight engine shutdown
Extract for convenience:

These FCTM are usually customized by operators / airlines before being used for crew training, so the recommendation may be improved or edited to better fit the company standards, but that's the idea.
The recommendation is not to be confused with the checklist for shutting down an engine, which depends on the cause of the problem. The checklists are part of the non-normal checklists (referenced in the extract above as NNC). E.g. if there is a fire detected, the crew will apply the related NNC which is found in the Quick Reference Handbook (QRH), like this one, page 170. Extract for convenience:

While the NNC in the QRH just provides steps like:
Thrust lever (affected side) . . . . . .  Confirm. . . . . . . . . .  Idle

the FCTM recommendation provides a way to train crews to ensure the affected side is properly identified.

This is similar to what I was taught, and some have the PIC guard the good engine(s) before the bad one is shut down as well.

The design of the cockpit itself shows that there is a procedure.
If you look in places like Airliners.net the upper panel in an Airbus, you will find that the extinguishers have a cover to prevent the unintentional activation.
Beyond that, a common approach is asking the pilot monitoring for confirmation about which engine has problems before pressing the button. Of course, to make it work, it has to be emphasized in the training process. I have been a witness in a situation where the pilot asking for confirmation had already the finger on the switch...if that is not corrected, you can be sure that, whatever the answer of the other pilot should be, he would press that button.

According to the 737NG flight manual that mins shared, the PM should have his hand on the switch/button when confirming with the PF that the correct one has been selected. Therefore, witnessing a situation where this happened doesn't seem all that unusual.


text:
Before a flight, what are the most important things to check in an aircraft (walkaround)?
During the pre flight inspection, usually the copilot checks many parts of the aircraft. Which are the parts and Why do they check them?

Chapter 3.3 of this document is a detailed explanation of what is done during the pre-flight inspection.

I have also seen the captain do his own walk-around after the FO has finished. I don't know if that's usual protocol or if those particular captains were just going the extra mile for safety.

Vote to leave the question open. Although the question seems to be "too broad" it has very concise answers. (We used to have a clear checklist for the walkaround)

Many things are checked on a walkaround. The pilot-in-command should do the walkaround, not the co-pilot. The main classes of items are as follows:
structural integrity; the aircraft must be sound and undamaged and ready to fly
sensors; sensors such as antennas and gauges should be undamaged and not have anything blocking them or adhering to them
clean flight surfaces; the control surfaces and flight surfaces must be smooth and clean; for example, the wings must not have ice on them
no leaks; hydraulic fluid, oil, fuel, and other critical liquids should not be leaking out of the aircraft
chocks, control locks and covers removed; all chocks, protective coverings and locks should be removed before flight and stowed
correct tire inflation; wear on the tires should not be excessive and the tires should be inflated properly
fasteners present and correct; all bolts, shims, nuts and other fasteners should be present, undamaged, and correctly installed
hatches and fairings secure; removable inspection plates and any other small doors, fairings and cowlings should be in place and secure.
lights ok; the lights on the aircraft should operate correctly and their lenses should have no cracks or other defects
blades ok; the propeller or turbine blades (as the case may be) should be perfect with no cracks or chips
Overlooking any of these sorts of items can cause (and has caused) serious accidents or incidents in flight or during takeoff and landing.

The other answer gives what is checked, but doesn't really touch on the "why".
Here are a few examples:
Birgenair 301 - Crashed shortly after take-off because it is believed a pitot tube was blocked by a wasps nest.
Aeroperu 603 - Crashed shortly after take-off because some tape was covering the static ports left there because of maintenance work.
Gulfstream IV - Crashed during take-off because the gust locks were not deactivated (Gulfstream had some role to play in this because the gust lock system is supposed to limit throttle movement but was not operating properly).
Twin Otter crashed just after take-off because the control lock was still in place.
Medical Flight crashed after take-off when it was refueled with JET-A instead of 100LL.
As a pilot, there is little you can do in the air when something goes really wrong, but there is a lot you can do on the ground to make sure that the aircraft is worthy to fly. Preflight inspection is one step to a successful flight and preflight doesn't just happen on the tarmac walking around the plane, there are also safety checks that happen inside the cockpit (like verifying the controls are free) and even more before you even see the plane (checking weather, routes, destination airports, NOTAMs, etc).

+1 for refocusing on the question and the why. Related: Inadequate Preflight

A good article, thanks.

The following is an (incomplete) list of checks carried out:

Engine - for any damage to blade (due to birdstrike etc.)
Tires - For any damage
Oil level indicator
Wings- Leading and trailing edges and tips for any damage
Any oil leaks
APU
Rear fuselage- tail skid area
Engine and fuselage- Any open cowling, exterior damage etc.
Probes- Any damage, ice etc.
Any other suspected damage.
In case of helicopters, condition of rotors for any damage.

A more detailed list can be seen elsewhere for B737 and A320.

One major item this list does not mention is fuel. Sumps, type, quantity.


text:
What does STERILE RUNWAY mean?
When a pilot receives the message : THE RUNWAY IS STERILE, what is the meaning?

Where did you hear that?

I heard on the liveATC, and also I had read on this link: http://www.avherald.com/h?article=44e8c132&opt=0

It means the runway has been thoroughly cleaned using detergents and wiped with alcohol towels.

@kevin, I wouldn't explain better than you, very clever answer!

A "sterile runway" indicates that all traffic has been cleared from the runway.
This can include both traffic currently active on the runway as well as potentially other inbound traffic on approach, or even elsewhere on the tarmac - if it is deemed disruptive.
A sterile runway is often used in emergency situations, such as when an airplane is coming in for an emergency landing. For the safety of both that plane as well as the others, the runway is cleared of any traffic.
That said, this term is not exclusive to emergencies. For example, the FAA requires 250 feet on either side of a runway to be clear of airplanes when a Commercial Airplane lands. An airport that is smaller and has tight taxiways might have an aircraft taxiing closer than that. To be within FAA compliance, they would need to ensure that the runway was sterile and that there were no active planes taxiing within that 250 feet at the time of the commercial plane landing. An example of this rule being observed includes this notice posted by Friedman Memorial Airport in Hailey, ID, where they adjusted their procedures in response to FAA determinations in order to accommodate commercial traffic and maintain a "sterile runway".

That's an excellent looking answer. If you can link in the FAR for the 250' clearance, that would be an excellent answer!

Thanks @FreeMan. I have gone ahead and added an example of the 250' clearance, by linking directly to a memo submitted by an airport noting this change, in accordance with FAA regulations to maintain a sterile runway.

It means that aircraft are not allowed to takeoff/land in that runway. From a British Antartic Survey Document on the Rothera Research Station:

BAS  procedures  require  a  sterile  runway  and  airspace  at  Rothera  for  all  periods where  the  BAS  DASH  7  has  passed  PNR  until  it has  landed.  Aircraft  will NOT be allowed to takeoff, land, hold in the overhead or the vicinity of the airfield during this period.


text:
How does a pilot receive weather information when overflying the oceans?
As the aircraft is too far from antennas and units, how do they be aware of weather changes or weather information along their route, or on the destination and alternate airports?

For local weather, they get part of the information from on-board weather radar. For both local and destination weather, they can also get information through satellite links.

Aircraft might be out of contact with ATC but will remain tuned to the service they are working.  If there is a significant weather change that might affect safety, they will transmit a report on that frequency.  ATC will not hear it, but anybody else working the same frequency, i.e. in the same part of the world, might hear it.  This is very common for turbulence reports on oceanic crossings.

There are satellite based services as well, such as XM Weather that provide accurate weather reports.

And before there were satellites & SATCOM, there was HF radio.  "Out of contact with ATC" -- not necessarily. Not usually, in fact.

It depends on what info you're after: During cruise I'm mainly interested in threats to the aircraft which normally manifest as echo on the weather radar (clear air turbulence being one famous exception) or by looking out of the window.

Do you want info on your destination and alternate airport you listen to a HF VOLMET station or ask ATC via HF (cumbersome and annoying due to often poor reception).
In our shiny new world we could also ask ATC via an CPDLC free text message. The controller simply uplinks you a message with the requested information.
Depending on your operator there might be a plethora of other information available via ACARS which - when equipped - can communicate via satellite. At my company we can get:

Updates on the winds aloft (important for fuel calculation)
Airport weather information (ATIS, METAR, TAF)
Sigmets

In general, the weather you really need is readily available. An ocean crossing is only a couple of hours. This timeframe is covered by the TAFs. So you shouldn't be too surprised when you don't have all that fancy stuff mentioned above and ask ATC once VHF COM is reestablished or you can receive a VHF VOLMET station.

Also other aircraft flying in the same area or route can give an update to the aircraft following


text:
How can pilots identify, in flight, the cracked layer(inner/middle/outer) from an impaired windshield?
Depending on the cracked layer, there would be some actions from the crew.
The inner layer seems to be simple to identify, but if the middle and/or outer layer is cracked, how will pilots identify the right crack's position?

It is possible to identify whether the crack affects the inner layer by sliding over it with nail or something sharp like pen. If the layer is cracked, the slight indenting in the surface can be felt.
As far as I can tell, there is no way to tell whether the outer or middle layer is affected with any useful degree of certainty. It is also not possible to ascertain how many layers are cracked. So usually the procedure is so that if the inner layer is not affected, you can continue and fix the issue at destination and if the inner layer is affected, you have to conservatively assume all layers may be affected and descend.

Shouldn't it be fairly easy to tell whether all the layers are cracked versus just the inner layer, by listening for the noise of air whistling out through a full-thickness-cracked windscreen and/or checking whether the pressurisation system is suddenly having more difficulty keeping the aircraft pressurised than it was pre-crack?

@Sean, I don't think there will be any significant airflow through a crack. Certainly not to either hear it over all the other noise in the cockpit and even less so for the pressurisation to be affected (the outflow valve is quite big opening, even a hole in the window would be small compared to it).


text:
How many aircraft can an ATCo control simultaneously, on procedural and radar service?
Aispace is separated in sectors, and each one has its own frequency. What's the airspace capacity for procedural and radar services, for a single sector?

There's probably not a specific number.   The answer will probably end up being "however many can do and maintain separation." Some sectors will include more complex maneuvering (more than one airport, several different approaches, both commercial and GA aircraft) so the airspace would have to be broken up into many smaller sectors with fewer aircraft in each to reduce workload. Whereas if you're talking about en-route, where the aircraft are not doing a lot of maneuvering the controller can probably deal with several times as many planes. If you think of arrivals at a busy airport, the airspace is broken into several different controllers, whereas often one guy in the tower is doing all of the landing clearances. That means he controls every single inbound flight whereas the approach controller is only juggling the portion that approach through his airspace. The workload per plane for the tower on landing is much lower since the approach controller will pass aircraft to him to him separated and already on ILS or with a visual on the runway. So all he is responsidle for is is making sure the runway is clear for each landing. In most situations tower only talks to the arrivals twice. Once to give clearance and then to pass them on to ground.

I vaguely recall hearing 35 aircraft per hour and 20 simultaneous for en-route sector under NMOC control, but I don't have reference handy, so I might be remembering it wrong.

The workload per plane on landing is much lower. I would disagree. Approach has to give vectors all the time. En-route might have flights that will never "bother" the ATCO unless there are too many descends and/or climbs.

@SteliosAdamantidis Had to reread what I wrote, but in that sentence I'm talking about the tower, not approach. I'll edit to make it more clear. I agree with you that approach would certainly be the most challenging position with the highest workload per plane because of the vectoring.

As already mentioned, airspace capacity is not a simple term. One very important aspect is aircraft separation. For example in procedural control separation is time based and (if I recall) it's 10 minutes flight time. That's definitely less capacity when compared to 10 miles for en-route and 6 for approach.
One other important aspect for calculating the capacity of a sector is the workload. Workload includes the time a controller spends talking (and listenign) to aircraft, coordinating flights, how much time is left for thinking and resolving conflicts etc. Eurocontrol has developed the CAPAN (capacity analyzer) methodology for calculating capacity.
Each sector is unique and has a unique capacity which the ANSP managing the sector should calculate. There is no "one size fits all" solution.


text:
Did Air Europe fly to Toronto from Lamezia Terme?
I am looking for more information regarding a flight from Lamezia Terme (SUF) to Toronto Pearson (YYZ) that according to some of the people I spoke to used to be operated by Air Europe around 1993.
I have researched wikipedia's Air Europe page and it looks like they have never even had an aircraft capable of servicing the 4,087 nm route.
Has any of you any idea of how I could retrieve more detailed information? For example, is there any way of knowing which airlines operated the route back in 1993?

This airline flew out of Toronto between 1990-1996 in the summertime only. It sold tickets through AlbaTours and it flew nonstop to Lamezia, Pescara, Rome CIA, Milan and Venice. It started off with the 757 making stops in Dublin/Shannon and then in 1992 it switched over to the 767 which made the journey nonstop.

Welcome to [Travel.SE]!  This is useful information, but it would be even better with citations.  If there are useful links you can provide, please edit your answer to include them.


text:
Why did this aircraft fly in this pattern over Southern Italy?
Why would an aircraft fly in the pattern shown in the image below? The location is Southern Italy.

An aerial survey most likely.

Why would they need such precise separation in the scanning pattern?

Aircraft with survey equipment (based not far from Sicily). Distance between tracks is likely linked to field angle of sensors, and angle required for 3D stereo imaging.

Google, Bing or Apple maps aerial photography?

@CF84 why would they NOT be following a regular pattern?

@mins, the model is the same, could even be the same aircraft

That flight pattern is almost certainly aerial surveying / mapping work and it's quite common all over the world.  Companies like Google, Bing, etc pay for low to medium altitude photography and surveying of areas.

There is another possible but far less likely answer. If an aircraft is equipped to detect radiological signatures, the baseline data collection patterns look like this.
So what does that mean? We live in a world which nuclear technology is used for many purposes, and is probably more prevalent than most people realize. Additionally, there are many sources of measurable, albeit low level radiation all around us emanating from various natural and man-made things. Granite, certain soil, radon, etc.
So the idea is the aircraft platform is equipped with specialized equipment to detect points of origin and dispersal rates and patterns radiation sources. Since real world examples of when this was used: The Washington State nuclear waste storage facilities tunnel collapse and subsequent leak, the Fukashima nuclear power plant meltdown, a terror attack using a dirty or small suitcase nuclear bomb.
So if an event occurs, the government will need to fully understand the level of magnitude regarding any radiation that would result. They would need to see how much, how large an area is impacted, which way is the radiation moving, and how quickly it is dissipating. But because there are those naturally occurring levels of various magnitude and scattered randomly throughout a region, a baseline measurement of the entire region in question must be completed.
Otherwise in a real world nuclear incident, the results would be inaccurate and possibly misleading based on not tapping into account what radiation was already present.


text:
Why does this NOTAM make me think GPS is unavailable?
First: I'm not a real pilot. I used an on-line flight planning tool, and in the brief was the following "GPS NOTAM":
GPS 11/032 ZSE NAV (CHLK GPS 15-15) GPS (INCLUDING WAAS, GBAS, AND
        ADSB)MAY NOT BE AVAILABLE WITHIN A 476NM RADIUS CENTERED AT
        360822N1173846W (BTY214059) FL400-UNL DECREASING IN AREA WITH A
        DECREASE IN ALTITUDE DEFINED AS:
        432NM RADIUS AT FL250,
        375NM RADIUS AT 10000FT,
        340NM RADIUS AT 4000FT AGL,
        253NM RADIUS AT 50FT AGL.
        DLY 2130-2230
        1511172130-1511182230

I must admit I don't understand most of this, but it seems like GPS is unavailable in what seems to be a huge inverted cone of space. What's going on here?

Interestingly, this appears to be those locations with approximately line of sight toward a ground-based location (the curvature of the earth limits the radius according to altitude).

See also: GPS Interference Testing CHLK GPS 15-15 - China Lake, California

This outage is due to department of defense GPS interference testing taking place 17-18 Nov 2015.  The interference generated may make the GPS signal unreliable and the outage cone described by NOTAM lets you know that you can't trust the GPS signal during this time.  This interference may be purposeful jamming or live testing of devices that may interfere with GPS to ascertain what level of interference occurs.

How did you come to this information? Is there something in the original text that tells you to go somewhere and look up something?

I was able to make it from the home page to the PDF you mentioned, but it seems unlikely that a pilot might know about this. Is this pretty common?

@Steve I just googled for gps scheduled outages.  Pilots that use GPS, particularly if they are familiar with RAIM and GPS NOTAMS are probably knowledgeable about that.

As a side note, non-pilots tend to believe that GPS is 100% available.  As a pilot though, I've had in flight loss of GPS a couple times and even was unable to take a planned trip due to a combination of a GPS outage and no other suitable approaches for the reported weather conditions.

@BrianKnoblauch Anyone who uses GPS a lot in mountainous regions or other areas where satellite reception may be limited knows that GPS isn't always available.

As does anyone who's ever tried to use Google maps for directions in Manhattan....


text:
What methods exist to detect airframe icing, and how do they work?
What are the primary methods used to detect ice on an airframe, and how do they work on at least a high level?

There are a few ways to sense ice on an airframe. The DOT has a document here that outlines the various types of sensors.
First and foremost planes have ice lights that project onto the wings so they can be visually inspected.
There are completely optical sensors that use a variety of methods to detect ice.
There are also some electro mechanical devices, here are a few examples, the rest are outlined in the DOT document.

Penny and Giles
The Penny and Giles system uses a probe type sensor that measures ice
  buildup in terms of Liquid Water Content (LWC). This system was
  designed specifically for use on helicopters and is available for all
  turbine-powered helicopters.
Rosemount
The sensing probe is driven magnetostrictively to vibrate at its
  resonant frequency of 40,000 Hz. As the ice detector enters an icing
  environment, ice collects on the sensing probe. The added mass of the
  accreted ice causes the frequency of the sensing probe to decrease in
  accordance with the laws of classical mechanics.
Sunstrand
The Sunstrand system uses a mounted probe with a sensing surface
  facing the airstream. Beta particles are released from a Strontium 90
  Radiation Source and are collimated by a specially shaped window in
  the probe housing. These particles pass across the sensing surface to
  a Geiger-Muller tube. High voltage is applied to the Geiger-Muller
  tube to enable it to detect the radiation emitted by the Strontium 90
  source. Ice accretion on the probe decreases the beta particles
  detected by the tube. When the particle count drops below a pre-set
  level, a pulse rate discriminating amplifier energizes an icing signal
  visible to the flight crew. At this time a heater inside the probe is
  activated, the ice is removed from the probe, and the probe is ready
  to begin another icing cycle.

Some of these will work in a static situation while others may require the passage from a non icing environment to an icing situation.


text:
How are operators of small UAS craft supposed to know about flight restrictions?
The FAA is requiring all operators of small unmanned aircraft systems between 0.55 and 55 pounds to register. This is to help ensure that operators of model aircraft and drones act in a responsible manner, etc.
In the Registration and Marking Requirements for Small Unmanned Aircraft document available from the FAA (PDF), there are examples given of drones being flown near wildfires that interrupted firefighting efforts, despite a temporary flight restriction for the area surrounding the fire.
It seems obvious to me that operating an RC aircraft near a wildfire might not be a good idea. However, "temporary flight restrictions" could exist in other cases that aren't quite so obvious. There is no requirement (as far as I know) for sUAS operators to check NOTAMs, aviation charts, etc.
How can an operator be sure they are in compliance in every situation? It seems like it might be very easy to violate some regulation inadvertently.

There is nothing that prevents sUAS operators (or even passengers-in-coach) from checking NOTAMs for where they're at :)

"FAA is requiring all operators of small unmanned aircraft systems between 0.55 and 55 pounds to register" - this is not true for those operating under 14 CFR Part 101 (hobbyist).

"There is no requirement (as far as I know) for sUAS operators to check NOTAMs, aviation charts, etc." - There sure is, see 14 CFR 107.49,  107.47 and 107.45

Information about current and future TFR areas is available from the FAA, even as an easy-to-read map. If someone is planning on flying a manned or unmanned aircraft, that should be on their list of things to check ahead of time.
As far as other airspace restrictions, we have a question detailing the different types of airspace. It would be worthwhile for a UAS operator to learn enough about reading charts to at least know the airspace in the area where they intend to fly.
Another option would be to attend ground school or at least do some amount of self-study. Just as pilots need to know how to operate according to the rules of the airspace system, UAS operators could benefit from the education.

Ah, an excuse for my wife of why I should attend ground school. Then, I might as well take a few hours with a CFI... :) +1 and probably an accept.

Checking with the FAA directly (either via the web or calling flight services) is the best bet, however there are also a variety of tools available to help with this more easily.
The FAA itself makes a mobile app called B4UFly that can provide a good amount of detail.  Additionally, the third party company AirMap has a good map system that is regularly updated and can be checked either online or via their mobile app. As an added bonus, airmap is able to automatically submit flight notifications for model aviation usage near select participating airports.


text:
What are possible explanations for fuel being expelled in this video?
In another question, I asked about whether or not a fuel spill would be reportable or not. The answer was "no", because the aircraft was not in flight.
What are the possible causes of the spill demonstrated by this video?

I can think of 4 possible causes, 3 of which can probably be discounted.

Tank venting. The fuel system is designed to deliberately "leak" if
the tanks are overfilled or, the fuel expands due to temperature
changes. Whilst I haven't seen this happen on a B767, I have seen it
on numerous other types and when it happens, it does not gush out
like it does in this video.  It's more of a seep of fuel which drips
off the underside.  Whilst it can be a lot of fuel, this video does
not fit a venting scenario.  Additionally, the flight crew would be
very familiar with venting which would be a normal event and would
not have abandoned the flight.
A fuel leak such as a ruptured pipe, a failed seal and so on.  I
would expect to see fuel ejected like this but only from a
pressurised part of the system, downstream of the fuel pumps.  The
location of this leak is not from a pressurised part of the fuel
system and in my opinion, there is simply too much fuel for it to be
a result of gravity.  It also appears to be coming from a nozzle
rather than seepage
As can be seen in this video, the source of the fuel is
coincident with the location of the fuel dump nozzle.  It is
possible that the crew accidentally activated the fuel dump but
unlikely (inconceivable?).  The switches are very clearly surrounded
with "don't touch this" markings and require two separate switches
to be activated.  Additionally, the jettison valve switches are
"guarded" such that you have to lift a spring loaded flap up in
order to be able to press the button.
The APU draws it's fuel from the left main tank. This flight was
close to the  maximum range of a 767 so  would have been at or close
to maximum fuel load. If the APU had been running for a long time,
longer than expected, it's possible that the crew started a fuel
transfer to balance the tanks by pumping fuel from the right tank to
the left tank and forgot to switch the transfer off.  This could
have pressurised the left tank causing fuel to overflow into the
surge tank and vent out (the surge tank vent is also very close
to the jettison nozzle).  I believe that this is the most likely scenario.

This is the only authoritative source I could find showing the fuel jettison switches.
All supposition of course but a strange incident.  I'm sure there may be other possible causes and I'm sure that comments and other answers might expand on this.

@mins Hey Mins, that's a good answer in my view and great information.  I don't want to steal your work.  Why don't you post it here?

This particular 767 does not have the fuel jettison nozzles installed (most 767-200s don't have them) and fuel can not be transferred between tanks from the cockpit (can be done from the fuel panel on the left wing). The fuel is discharging from the vent in the surge tank, I suspect this happened during manual refueling as the overfill sensors would shut off fuel to that tank in auto.
The only other likely scenario would be one or more of the check valves between the left tank fuel pumps and center tank pumps had failed open with fuel in the center tank and the center fuel (override) pumps on.

Welcome to Av.se!


text:
Why shouldn't the pilot change the aircraft's configuration while avoiding windshear during landing?
According to the procedures, when going around, due to windshear, pilots shouldn't change the aircraft's configuration, such as flaps position and landing gear extension. If changing, would the aircraft lose the lift? why?

Could you elaborate on the "procedures" or provide a link to them? That would help a lot.

The SOP requires that during a go around, due to windshear, the crew should not change the aircraft's configuration, until leaving the windshear.

You leave the gear down in case you touch down while executing the go around. You leave the flaps alone so as to not unbalance the aircraft while you're manoeuvring the aircraft.

During extension and retraction the gear drag is substantially higher than in the extended position. This has two reasons:

When the gear moves, the first thing to happen is that the big bay doors open. They are also the last to close after the gear has reached its new position. During that time, the large cavity of the gear bay will cause additional drag, sometimes as much as half of the drag of the extended gear.
When the wheels are close to the fuselage, their drag contribution is higher than when they are at some distance due to higher interference drag.

Figure 38 from S. Hoerner's Fluid Dynamic Drag, Chapter 13 page 14.
Note that after landing gear extension the biggest doors close again. The time it takes to retract the gear is similar to that where windshear will cause the biggest airspeed loss. Consequently, cycling the gear will increase drag over that of the extended configuration, and any improvement in aerodynamic quality due to a retracted gear can only be gained after the worst is over and the aircraft will speed up and climb anyway, regardless of gear position.
Also, changing the configuration will be distracting in a stressful situation, and the risk of a wrong configuration change is increased. It is better to let the pilot focus on flying the plane than to burden her/him with additional work.

As far as landing is concerned, it is better to leave the landing gear down because if something goes down and the aircraft touches the ground, it is better to do so with the landing gear rather than the aircraft fuselage. Also, the retraction process may increase drag, not what is desired.
During landing, the retraction of flaps (which may be already at their max) can cause loss of lift (as you noted). Reduced airspeed due to windshear causes loss of lift; retracting the flaps in this condition is not desirable.
There is also the point that during the critical moments when the pilots are trying to pilot the aircraft during wind shear, their attention should be in flying the aircraft and not in fiddling with controls.
From FAA Advisory Circular 00-54 Pilot Windshear Guide:

CONFIGURATION
Maintain flap and gear position until terrain clearance is assured. Although a small performance increase is available after landing gear retraction, initial performance degradation may occur when landing gear doors open for retraction. While extending flaps during a recovery after liftoff may result
  in a performance benefit, it is not a recommended technique because:
1) Accidentally retracting flaps (the usual  direction of movement) has a large adverse impact on performance.
2) If landing gear retraction had been initiated prior to recognition of the encounter, extending flaps beyond a takeoff flap setting might result in a continuous warning horn which distracts the crew.

One thing worth mentioning is that in some GA aircraft, the flap lever and the gear lever have a similar feel, and while the pilot thinks they are pulling the gear lever they may be retracting the flaps. Its best to leave both alone and focus on flying until enough airspeed and altitude are gained to start retracting them in stages.

As usual, Peter's answer is correct. However, I wanted to address the last part of the question regarding if lift would be lost, since I didn't see a direct answer to it in the other answers:
Yes, the aircraft will lose lift if you retract the flaps. The whole purpose of flaps is to increase lift at low airspeeds in order to allow the aircraft to takeoff and land with lower airspeeds than it would be able to use if it had no flaps. However, flaps also increase drag, which is why you retract them once the airspeed is high enough to not need them. During a landing, flaps will normally be set at or near their maximum extension, which allows the aircraft to fly quite a bit slower than it would otherwise be able to fly. If you suddenly retract the flaps while flying at final approach speed, you will lose a lot of lift and potentially even stall the aircraft. Needless to say, that's not good on final approach, especially if you're trying to go around.
Note that flaps increase both lift and drag at any (positive) airspeed, so retracting them will always result in less lift, but also less drag.

Well, the configuration at landing is for low speeds, if the flaps are pulled up, the airplane might stall because of low speed air separation and might take the necessary lift away to get get away from the windshear. And as a comment above says, the flaps also help with stability when manoeuvring the airplane at low speeds. Gears are left down in case of unwanted touchdown (This is windshear, so it might happen).


text:
Can we use the term CONTAMINATED RUNWAY for other meanings, such as: oil spill or debris on the runway?
Contaminated Runway is used to say that the runway surface area (25%) is covered by 3.0 mm or more of: water, slush, snow and ice. But is it also possible to use this term to say about: heavy rubber, oil spill, debris or other substances are on the runway surface?

Related: How are runway conditions measured?

From the FAA Pilot/Controllers Glossary Book:

CONTAMINATED RUNWAY− A runway is
  considered contaminated whenever standing water,
  ice, snow, slush, frost in any form, heavy rubber, or
  other substances are present. A runway is contaminated
  with respect to rubber deposits or other
  friction-degrading substances when the average
  friction value for any 500-foot segment of the runway
  within the ALD fails below the recommended
  minimum friction level and the average friction value
  in the adjacent 500-foot segments falls below the
  maintenance planning friction level.

(See also ICAO Circular on Runway Surface Condition Assessment Measurement and Reporting) Thanks to mins.
So this covers rubber and oil, but not debris.
However, from searching the glossary there are no instances of the word "debris" in the document. Usually if debris or oil were noticed on a runway, ATC would close the runway (issue a NOTAM) and then use an alternate runway until the debris or oil were cleaned up.
From a pilots perspective, if you notice debris on the runway just tell ATC (provided you didn't hit it), and they will close the runway for a FOD (foreign object debris) check. My local airport does this usually twice a day or more, typically by running a car down the runway looking for debris.

Your quote does say "or other substances are present." so could apply to the things that he asked about.

@Lnafziger Its possible, although a contaminated runway doesn't necessarily mean it needs to be closed, whereas something like debris would require it.

@mins Thanks, the FAA Glossary usually points out differences with ICAO terms "Because of the international nature of flying, terms used in the Lexicon, published by the International
Civil Aviation Organization (ICAO), are included when they differ from FAA definitions. " I'll add your link to my answer for clarity.

In the US, I was specifically taught that ATC does not have the authority to close (or especially open!) a runway—only the airport authority may do that. Though ATC can certainly withhold a landing or takeoff clearance if they feel the operation would not be safe.


text:
Windshield to prevent laser strikes
Is it possible to prevent/avoid laser beams with new technologies on windscreem?

Is it technically doable to shield only coherent light? Probably yes. Is it a good idea? Probably not; what if other plane's or the airfield's or PAPI or whatever light/beacon/whatever is based on coherent light, too? You wouldn't see it.

Only if you know the laser wavelength.
If the windshield uses a color filter, it can attenuate the light intensity at one wavelength while being transparent for other wavelengths, so the pilot can still see what is going on outside. The colors will look strange, but laser beams of the filter wavelength would have less intensity when viewed through this screen. This only works, however, if the laser wavelength is known beforehand, so the right filter can be used. All other light signals, approach lights and what not would need to use sufficiently different wavelengths so they are still visible.
Think of an approach in fog, rain or haze. Sometimes all the pilot sees is a faint glow - if the filter takes this away, the pilot will notice the lights only later, when they are closer and there is less time to react.
The other alternative is synthetic vision. The cockpit has a row of screens which show the images of cameras in the nose of the aircraft. This was already investigated by NASA for supersonic passenger aircraft, but met resistance from pilots. The reduced contrast of screens will make lasers merely a nuisance, but not harm the pilot. Clever software could even filter out too bright light sources.

There is actually a legitimate use of lasers to warn pilots, its used by NORAD around the Washington DC ADIZ, but at wavelengths that are not harmful to the eyes.

They were discussing the recent incident involving a laser on the radio today, and the "expert" they had in the studio commented that you can buy polarised glasses, which protect the pilots eyes from laser strikes. is this true, and could the same technology be used to create a windscreen? Does this offer greater protection than the colour filter method you mention?

@GavinCoates Sure, you can create a coating for the windscreen, but also note how those glasses aren't entirely transparent. I'm not sure the reduction in nighttime visibility is worth the relatively small chance of getting hit by laser beams. Plus the filter can only stop one wavelength, if somebody uses a different wavelength laser, then the coating won't do anything. Not to mention it will filter without discretion as to it being a laser, or just something the same color, so effectively you may be making the pilot red or green color blind...


text:
Some wing parts designation

Under the trailing edge, there are 3 features, as seen in the picture. What's the name and the purpose of them?
The chord line is the distance between the leading and trailing edge.
What's the name of the upper and the lower surface of a wing?

@Steve He is asking for a little more than just that.

The three bodies are the housings for the flap actuators and they do just that. There is no special name for the upper and lower wing surfaces that I know of or can find, just "upper" and "lower".

The sharp pods are called anti-shock bodies or flap track fairings. See this question for further information. Simply put, htey are there to reduce drag- transonic drag by smoothly varying the cross sectional area (Whitcomb Area rule) and by covering the flap actuators.
The straight line connecting the wing leading and trailing edges is called chord line; the distance between them is called chord length (both are usually called chord).
The upper and lower wing sufraces are called, well, upper surface and lower surface of wing.


text:
Why does the cross sectional area of the air going into the inlet of a turbo fan changes during take off and cruise?
This is the first time I see this and I'm trying to make sense of it, I was reading these slides:
https://slideplayer.com/slide/13267627/
I'm having trouble understanding why the area of the streamtube of air going into the inlet is much larger than the inlet during take off than during cruise. Also why the mass flow rate and thrust is much bigger during take of than in cruise?
I'm trying to relate it to the pressure in the ground being much bigger in the ground than at cruise altitude, but that makes it even more confusing because the fan creates lower pressure zone to suck in air right?, but lower pressure is more related to higher gas volume, so I'm completely lost.

why [is] the area of the streamtube of air going into the inlet [] much larger than the inlet during take off than during cruise?

Because at low speed the engine has to suck in air while at high speed the air is pushed into it. So much actually that only the core of the streamtube can be ingested and the rest spills over the intake lips.

why [is] the mass flow rate and thrust [] much bigger during take of than in cruise?

Because cruise happens in much less dense air. A cubic meter of air on the ground weighs roughly three times as much as a cubic meter at altitude.

"Because cruise happens in much denser air"...you mean "less dense air", right?

@Gabe Oh boy, it was late when I wrote this ... of course you are right.